1. Field of the Invention:
The present invention relates to concrete reinforcing steel bars or wires useful for reinforcing concrete structures, such as concrete structures built on seashores and marine concrete structures, and concrete bridges, which are exposed to sea salt particles and sea-water splashes, and very excellent in preventing deteriorations or decays of these concrete structures.
2. Description of the Related Art:
In recent years, keen attentions have been paid in various fields of industries to the problem of concrete decays due to cracks in reinforced concrete structures built with use of sea sand or built on seashores, and various preventive methods have been proposed and indeed some of them have already been put into practice.
The principal cause for the concrete decays or deteriorations has been found to be attributable to the fact that steel bars or wires embedded in the concrete structure are corroded by salts contained in the sea sand mixed in the concrete or by the sea salt particles permeating into the concrete structures built on the seashores or in oceans and increase in their volume by about 2.2 times due to the corrosion, and the concrete fails to stand against the expansion force of the corroding steel bars or wires and cracks along the embedded reinforcing bars or wires, and that when the cracks grow about 0.2 mm or larger, exterior corrosive media, such as oxygen, salts, and carbon dioxide in the air penetrate through these cracks into the interiors of the concrete structure where the reinforcing bars or wires are embedded to promote the corrosion of the bars or wires, or to accelerate neutralization of the concrete, causing premature decay of the concrete structures.
For the purpose of preventing such decays of concrete structures, the present inventors have conducted extensive studies and experiments to improve the salt resistance of the reinforcing steel bars or wires by controlling their chemical composition and developed concrete reinforcing steel bars or wires having remarkably improved salt resistance, as disclosed in Japanese Laid-Open Patent Applications Nos. Sho 57-48054 and Sho 59-44457 and widely published in "OFFSHORE GOTEBORG '81", Paper No. 42, Goteborg Sweden, 1981; "CEMENT CONCRETE" No. 434 (1983), Pages 23 to 31; "CORROSION OF REINFORCEMENT IN CONCRETE CONSTRUCTION" Page 419, 1983; and "KENCHIKU NO GIJUTSU SEKO" (Practice for Building Construction) No. 229, 1985, Jan. Pages 155 to 164 published by Shokokusha, Japan.
Also details of the salt resistance mechanism at initial stages of steel compositions of the reinforcing bars or wires which contribute for improving the salt resistance of reinforcing bars or wires per se are reported in these technical papers.